A Transport Protocol for Multimedia Wireless Sensor Networks Duarte - - PDF document

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A Transport Protocol for Multimedia Wireless Sensor Networks

Duarte Meneses, António Grilo, Paulo Rogério Pereira

Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa

27-06-2011 1 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks

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Introduction – Wireless Sensor Networks

• Typically a high number of autonomous nodes with sensors and RF

communications.

• Cooperate in a common task retrieving sensor data such as:

temperature, humidity, light, image, video, etc.

• Data is normally forwarded wirelessly to a sink node
• Used in surveillance and security, industrial process control, military

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• Used in surveillance and security, industrial process control, military

applications, domotics, monitoring, etc.

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Other networks

Mobile devices

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Motivation

• Protection of critical infrastructures, namely electrical energy

distribution infrastructures

• Multimedia data from cameras is routed multi-hop to the sink
• WSN advantages: ease of installation, configuration, flexibility, low

power

• TCP: end-to-end, loss assumed as congestion, RTT delays

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• TCP: end-to-end, loss assumed as congestion, RTT delays
• New transport protocol tailored for WSN: DTSN.

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Objectives

Transport protocol for WSN with the following characteristics:

• Adapted to embedded systems
• Battery operated
• Runs on Linux
• Support reliability

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• Support reliability
• Optimize multimedia data transfers, particularly real-time

video

• Support several simultaneous applications
• Support security mechanisms
• Ease of use through an API

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Purpose: Reliability Guarantee and/or Congestion Control

Several different characteristics and mechanisms:

• upstream/downstream communication
• Loss feedback through: ACK, NACK, iACK
• Lost segment detection: sequence number continuity or

timers for each segment

Transport Protocols for WSN

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timers for each segment

• end-to-end or hop-by-hop

recovery

• Two types of target

applications: sending events or sending large data volumes

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• !
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• Sessions identified by

a Session Number, Application ID, source and destination addresses

• Feedback when

requested by the source through an DTSN

DATA 0 DATA 3 DATA 2 DATA 1 DATA 8 DATA 4 DATA 6 DATA 5 DATA 7 + EAR DATA 10 DATA 12 DATA 11 DATA 9 DATA 13 DATA 15 + EAR DATA 14 DATA 3 DATA 2 DATA 4 DATA 6 DATA 5 DATA 7 + EAR DATA 10 DATA 12 DATA 11 DATA 9 DATA 13 DATA 14 DATA 3 DATA 4 DATA 6 DATA 5 DATA 10 DATA 12 DATA 11 DATA 13 DATA 14 EAR 15 DATA 7 + EAR NACK 0, <0,1,2,3>

Node 1 Node 3 Node 2

NACK 0, <0,1,2>

Node 4

DATA 3 EAR Timeout

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source through an Explicit Acknowledgement Request (EAR)

• Losses detected

through the sequence number continuity

• Selective Repeat

retransmission hop- by-hop: intermediate nodes cache packets

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EAR 15 EAR 15 EAR 15 NACK 0, <0,1,2,8,9,10,12,15> DATA 10 DATA 12 NACK 0, <0,1,2,8,9,15> NACK 0, <0,1,8,15> DATA 0 DATA 1

t

DATA 8 DATA 15 Flow Control Timeout EAR 15 EAR 15 EAR 15 DATA 0 DATA 1 DATA 8 DATA 15 DATA 0 DATA 1 DATA 15 NACK 7, <8,10,12> NACK 7, <8,12> NACK 7, <> DATA 2 DATA 9 DATA 2 DATA 9 DATA 10 DATA 8 DATA 12 DATA 8 DATA 12 DATA 17 DATA 16 DATA 18 DATA 20 DATA 19 DATA 17 DATA 16 DATA 18 DATA 19 DATA 17 DATA 16 DATA 18 DATA 19 DATA 21

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Expected number of links crossed: Expected number of transmissions per

Probabilistic Model

Success probability:

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packet: Generalized formulas for different losses in each link:

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Expected number of transmissions when packets are cached with 50% probability:

Probabilistic model 2

"# "" "$

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27-06-2011 8 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks % & ' "# #(#" #(#$ #(#) #(#* #(#+ #(#, #(#% #(#& #(#' #("

• ..$+/-0
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• ..

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• The protocol is generic: can work over several wireless

technologies and hardware

• The Silex SX-560 was used.
• Supports Wi-Fi 802.11a/b/g.
• 200 MHz 32-bit ARM processor
• 16 MB RAM

Development Platform

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• 16 MB RAM
• 8MB Flash
• Runs Linux
• 792 mW average power
• 49.6 x 34.3 x 9.65 mm
• Developer’s daughtercard with

USB, serial, SPI, GPIO, Ethernet, power

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General Architecture

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• DTSN implemented as a single daemon process for all node

types: source, receiver and intermediate nodes.

• Clients use the protocol through a library that connects to the

daemon through UNIX sockets

• Several configuration parameters may be adjusted in a

configuration file

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• Dynamic library
• Interface similar to the Unix sockets interface
• Simple operation, with most work done centrally in the

daemon

• The application can receive asynchronous events
• Threads, blocking and exclusive access implemented

API

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• Threads, blocking and exclusive access implemented

through the pthread library

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• Header present in all packets:

Bit Flag ACK 1 NACK 2 EAR 3 DATA 4 RESEND 5 ENDSESSION 6 (not used 7 (not used)

DTSN Sessions 1

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• Soft unidirectional sessions, identified by <App ID, Session No,

Src Addr, Dest Addr>. No connection establishment: the applications just creates the session and start sending packets

• A complete session description is maintained with buffers, timers,

ID, mode, etc.

• The session can be kept internally after being closed by the

application

7 (not used) 27-06-2011 12 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks

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• Sliding windows mapped into circular buffers
• Both windows synchronized.
• Simple flow control by limiting the number of unconfirmed

packets

DTSN Sessions 2

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sender receiver

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3 6 8 367 3 6 6 365 364 3 6 3 362 361 360 3 5 9 3 5 8 369 3 7 371 372 373 374 3 7 5 3 7 6

Aplication

Oldest unconfirmed segment Last segment sent Where the next segment will be placed

DTSN 368 367 3 6 6 365 364 363 362 361 360 359 3 5 8 3 6 9 3 7 371 372 373 374 375 376 Aplication

Next expected segment Last segment received Next segment to be read by the application

DTSN

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• Intermediate nodes participate in packet recovery
• Space uniformly divided through existing sessions
• Packets kept in linked lists
• FIFO for each session
• Other caching policies for

2 34 2 34 2 34

• Cache

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• Other caching policies for

future work

• Packets eliminated with

ACK/NACK/ENDSESSION received if security is not used

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34 5 ((( 34 5 ((( 34 5 (((

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• Activity Timeout: used when the sender window is not empty or

full, and no new data is received from the application, to trigger sending an EAR.

• EAR Timeout: used when an EAR was sent and the sender is

There are 5 timers with different periods and purposes. There is always a single one active at each time for each session. Timers

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• EAR Timeout: used when an EAR was sent and the sender is

waiting for a NACK/ACK.

• Wait Timeout: used when the sender window is empty to destroy

a session without activity.

• Flow control Timeout: Active when the sender window is full
• Receiver Activity Timeout: only timer used by the receiver,

restarted every time a packet is received from the source.

sender receiver

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Security 1

• Most WSN protocols ignore the security issues, assuming

it is assured by lower layers (e.g. MAC).

– This may be energetically inefficient, as only some (important) packets require security

• Attacks possible by packet replication or injection

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– Purpose: denial of service, data manipulation, reduce node lifetime

• Security requires some overhead, increasing energy spent
• Security is optional: the application decides
• The DTSN security extension uses symmetric

cryptographic functions (HMAC based on the SHA-2 hash function).

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masterkey “ACK master key” |AppId ACK master key NACK master key HMAC HMAC HMAC HMAC

KACK

(n)

KNACK

(n)

“per packet ACK key” |n HMAC HMAC

MICNACK

(n)

MICACK

(n)

<packet contents>

Message Integrity Code (MIC) and key computation: Security 2

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Packet format:

“NACK master key” |AppId “per packet NACK key” |n <packet contents>

27-06-2011 17 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks

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• M-DTSN functionality implemented, allows restarting a
• session. The following actions are performed:
• Discard all packets in the sender window and change the session nr.
• Intermediate nodes also discard cached packets
• The receiver eliminates data from the window and notifies the

application Multimedia

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3" 3$ 3) 3" 3$ 3)

• !

;3 ;3. ..3 ..3.

• A new session is implicitly started without additional overhead
• The idea is to give up
• n sending data from

a frame after a temporal limit set by the application.

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• A module to simulate a sensor network over a LAN was developed
• Routing is made based on DTSN addresses
• Arbitrary bit error rates can be configured
• A 1.95 MB file was transmitted over 7 hops
• 5 situations tested:
• 512 bytes payload with and without cache
• 512, 350 and 200 bytes payload with security and cache

Simulation

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512, 350 and 200 bytes payload with security and cache

• Single hop between a PC and a Silex to measure throughput

27-06-2011 19 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks " "'$(",&()(" " "'$(",&()(" * "'$(",&()(* + "'$(",&()(+ , "'$(",&()(, % "'$(",&()(% & "'$(",&()(& " "'$(",&()(" $ "'$(",&()($ ) "'$(",&()()

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$)$ "&% "&, "'# ",& "+) "," *,& **+ )%$ )', )*' )$" )$* %', ,+, %%, ,$* *%, +$, *+$

$## )## *## +## ,## %## &##

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Results 1

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27-06-2011 20 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks

% %(" %($ %() %(* %(+ %(, %(% %(& %(' #(#" #(#* #(#% #("

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• Comparing the 5 tested scenarios:

Results 2

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27-06-2011 21 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks

200 512 #(#) #("* #($* #()% #(#, #($$ #()' #(#& #()) #(#& #($, #(*, #(#& #()$ # #(" #($ #() #(* #(+ $(*=#, '(,=#, "(%=#+ $(+=#+

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Results 3

#("* #(", #("& #($ #($$ #($* #($, #($& #()

% "" "$ ") "* "+ ", "% "& "' $# $" $$ $) $* * +

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27-06-2011 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks 22

# #(#$ #(#* #(#, #(#& #(" #("$ $(*=#, '('=#, "(%=#+ $(+=#+

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Results 4

PC Silex Silex PC DTSN 10.36 s (1.51 Mbps) 8.03 s (1.94 Mbps) DTSN with security 10.97 s (1.42 Mbps) 8.22 s (1.90 Mbps)

• 1.95 MB file transfer over a 10Mbps Ethernet
• 1 hop, no link errors
• Performance results:

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• High overhead in the communication between the protocol

and application

• The security option impact on performance is not significant

DTSN with security 10.97 s (1.42 Mbps) 8.22 s (1.90 Mbps) DTSN without delivery to application on Silex 4.69 s (3.33 Mbps) 8.03 s (1.94 Mbps) TFTP (UDP) 12.0 s (1.30 Mbps) 79.9 s (0.20 Mbps) FTP (TCP) 3.00 s (5.20 Mbps) 5.17 s (3.02 Mbps)

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Results 5

• Optimized version performance results:

PC -> PC

(Fast Ethernet)

[Mbps] PC -> Silex

(802.11b)

[Mbps] Silex -> PC

(802.11b)

[Mbps] Silex -> Silex

(802.11b)

[Mbps] DTSN 83.20 2.36 3.21 2.69

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• Much better performance
• Silex CPU performance is a limitation

27-06-2011 24 NGI'2011: A Transport Protocol for Multimedia Wireless Sensor Networks

DTSN 83.20 2.36 3.21 2.69 DTSN with security 62.42 1.68 2.02 1.87 FTP 88.68 5.73 4.47 4.69 TFTP 10.96 0.34 0.29 0.17

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Conclusion

• A transport protocol for real-time streaming in WMSN was

successfully implemented and tested.

• Tests prove the correct operation and show that DTSN is

efficient in reducing the number of transmissions in WMSN, thus saving energy.

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WMSN, thus saving energy.

• Future work:

– Dynamic parameters, such as timeouts, window and cache sizes – New caching policies, for instance by storing packets with probability less than 1, according to the distance to destination, etc. – raw sockets – BeagleBoard

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